Advertising and other display devices utilizing differential temperature and pressure to cause vapor bubbles of a volatile liquid to move up a tube are known. For example, U.S. Pat. No. 1,503,564 to Menzies consists of a transparent tube connecting two reservoirs containing a volatile liquid. The apparatus uses the temperature differential caused by external heating of one side of the device to cause the expansion of the volatile liquid vapor resulting in an increase of internal pressure. This increased pressure causes the vapor of the volatile liquid to rise through the transparent tube to the upper reservoir where it is cooled by the evaporation of liquid absorbed by a wick dipping in water of a receptacle. This cooling then causes the condensation of the vapor into liquid, whereupon gravity pulls the liquid down the tube. However, this device lacks a reliable method far generating and controlling the rate of cooling and heating, and requires a low humidity in the ambient air to operate.
U.S. Pat. No. 2,453,177 to Abramson is an example of devices that utilize an active heat source to boil a volatile liquid and cause bubbling. In this patent, heat is provided by an electric light bulb placed in proximity to the volatile. liquid. The bubbles rise to the top of the device where the vapor cools and becomes condensed upon exposure to atmospheric air (the temperature of which is lower than the boiling point of the liquid in the lower part of the device).
The Abramson device also lacks a controlled mechanism to regulate the heating and cooling of the liquid. For example, this device could explode if the heat provided by the light bulb is too great. It also is concerned only with the creation of bubbles, and is not directed toward an apparatus that gives the illusion that the liquid is rising through a tube.